1. Field of the Invention
This invention deals with a self-tuning controller for a seismic source vibrator for controlling the output of the servo valve or the actuator through a feedback network, and more specifically, it describes a controller for dynamic control of the servo valve or the actuator, the controller including a state variable technique with inaccessible states controlled through a model with observers.
2. Description of the Prior Art
In prior art controllers, very little has been done to optimize the dynamic response of the servo valve or the actuator (mass, column, pad). In some systems, a series compensator (a lead-lag network) is inserted in the forward path of the servo valve control loop to control the dynamic response of the servo valve, but such systems rely on operator judgment to adjust a potentiometer to select an appropriate feedback level. Because servo valve dynamics are sensitive to the temperature of the hydraulic fluid, a feedback setting selected early in the morning may not produce the same vibrator dynamic response after several hours of operation. Changes in the dynamic response of the vibrator system may result in degraded performance of the vibrator.
Early systems also have not compensated for source generated distortion. For example, distortion may be due to the non-linear nature of the equations relating servo valve spool position, hydraulic flow and the pressure drop across the servo valve. A method of reducing unwanted distortion is to monitor the pressure being applied to the actuator and to use it as a feedback in a control loop. The actuator force is the force exerted by the hydraulic fluid upon the reaction mass and in an equal and opposite direction to the column. By reducing the distortion in the actuator force waveform, the energy imparted to the earth through the column and the earth coupled pad or marine transducers has less distortion.
Prior art systems have dealt with various feedback remedies for controlling the force waveform imparted to the earth. However, these prior art systems have not availed themselves of state variable feedback coupled with Kalman filter techniques, including observers, for instantaneous feedback response relating to the performance of the servo valve and the actuator.